CBD-1062:  include voltron revision in emitted manifest, if 4th argument

Change-Id: I12a4f80e606ac983ac4399f4032542a3b9fe8c67
Reviewed-on: http://review.couchbase.org/28421
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>